United States Nuclear Regulatory Commission - Protecting People and the Environment

Information Notice No. 92-06: Reliability of ATWS Mitigation Systems and Other NRC-Required Equipment not Controlled by Plant Technical Specifications

                                UNITED STATES
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF NUCLEAR REACTOR REGULATION
                           WASHINGTON, D.C.  20555

                              January 15, 1992


NRC INFORMATION NOTICE 92-06:  RELIABILITY OF ATWS MITIGATION SYSTEM AND 
                               OTHER NRC REQUIRED EQUIPMENT NOT CONTROLLED
                               BY PLANT TECHNICAL SPECIFICATIONS


Addressees

All holders of operating licenses or construction permits for nuclear power 
reactors.

Purpose

The U.S. Nuclear Regulatory Commission (NRC) is issuing this information 
notice to alert addressees of the importance of maintaining the reliability 
of equipment required by NRC regulations but not addressed in plant 
technical specifications.  It is expected that recipients will review this 
information for applicability to their facilities and consider actions, as 
appropriate, to avoid similar problems.  However, suggestions contained in 
this information notice are not NRC requirements; therefore, no specific 
action or written response is required.

Background

In 1983, the Salem Nuclear Generating Station experienced an anticipated 
transient without scram (ATWS) event.  Following this event, efforts then in 
progress to establish requirements to address ATWS events were completed, 
and the NRC issued, on June 1, 1984, Section 50.62 of Title 10 of the 
Code of Federal Regulations (10 CFR 50.62), "Requirements for reduction of 
risk from anticipated transients without scram (ATWS) events for 
light-water-cooled nuclear power plants."  This regulation required that 
each reactor have equipment, diverse from the reactor trip system, that 
would automatically initiate actions to mitigate the consequences of an 
ATWS.  The regulation also required that the equipment for this system be 
independent from the existing reactor trip system and be designed to perform 
its function in a reliable manner.  The NRC did not require licensees to 
address the operability of this equipment in plant technical specifications 
nor did the NRC require that this equipment be designated as safety-related.  

Description of Circumstances

To meet the requirements of 10 CFR 50.62, the Houston Lighting and Power 
Company, the licensee for the South Texas Project (STP), installed ATWS 
mitigation system actuation circuitry (AMSAC).  In May and June of 1991, 


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                                                            IN 92-06
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the NRC inspected the implementation of this system at STP, Units 1 and 2, 
and identified three situations in which the reliability of the ATWS 
mitigation system had been compromised.

While inspecting Unit 2, the NRC found that the licensee had left open the 
switches for the interface circuit between the AMSAC system and the 
auxiliary feedwater (AFW) system.  These open switches disabled the 
automatic AFW flow initiation feature of the AMSAC, an important part of the 
ATWS mitigation system.  The NRC also found that the licensee had bypassed 
the automatic initiation feature of the AMSAC system, causing the system to 
be inoperable, at least 15 percent of the time that the system was designed 
to be operable.  While inspecting Unit 1, the NRC found that the licensee 
had bypassed the automatic initiation feature of the AMSAC system 36 percent 
of the time that the system was designed to be operable.  The NRC issued the 
licensee a Severity Level III violation and assessed a civil penalty.

The NRC also issued the licensee for Comanche Peak a Severity Level IV 
violation because the ATWS mitigation system was bypassed for approximately 
10 days while the reactor was operating at full power.

Discussion

In April 1985, the staff issued Generic Letter 85-06, "Quality Assurance 
Guidance For ATWS Equipment That Is Not Safety-Related," to provide explicit 
quality assurance guidance for the nonsafety-related equipment encompassed 
by the ATWS rule.  Although much of the equipment required by 10 CFR 50.62 
is not designated safety-related, it does perform an important safety 
function if the plant's primary reactor protection system fails.  The 
regulation was issued to reduce the risk posed by such an event.  The NRC 
considers the failure of licensees to comply with this regulation and to 
ensure that the ATWS mitigation system and equipment function reliably to be 
a significant regulatory concern.

The events described above indicate that licensees may not place an 
appropriate level of priority on resolving problems with the ATWS mitigation 
system because it is not a safety-related system and because the plant's 
technical specifications do not govern its operability.  However, 
maintenance of this system is of high priority and appropriate because such 
action assures the important safety function of the system and satisfies the 
requirements of 10 CFR 50.62 for the system to function reliably.  Actions 
taken by licensees to ensure the reliability of the ATWS mitigation system 
have included performing timely surveillance testing, completing repairs and 
preventive maintenance promptly, implementing necessary modifications, and 
updating procedures to reflect system changes.  

Plant technical specifications only address the minimum personnel and 
equipment requirements for the various modes of plant operations.  However, 
it is important that licensees maintain equipment and systems required by 
NRC regulations, to ensure their reliability, even though they are not 
addressed by a plant's technical specifications.  
.

                                                            IN 92-06
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This information notice requires no specific action or written response.  If 
you have any questions about the information in this notice, please contact 
one of the technical contacts listed below or the appropriate Office of 
Nuclear Reactor Regulation (NRR) project manager.




                                   Charles E. Rossi, Director
                                   Division of Operational Events Assessment
                                   Office of Nuclear Reactor Regulation


Technical contacts:  R. Evans, RIV
                     (512) 972-2507

                     C. Paulk, RIV
                     (817) 860-8236

                     J. Mauck, NRR
                     (301) 504-3248

Attachment:  List of Recently Issued NRC Information Notices
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